In recent years, for example, beam forming or beam steering has been used as phased array systems for millimeter wave bands. Such phased array systems are used for, for example, communications between a base station and a terminal or a vehicle-mounted radar in fifth-generation mobile communication systems (5G: 5th Generation).
Such phased array systems include a phase shifter. A signal having a desired phase (an intermediate phase of two signals) is generated by controlling the gains of two amplifiers in combination, the amplifiers amplifying two signals having a phase difference of 90°.
As described above, a phase shifter applied to a phased array system generates a desired phase signal by controlling the gains of amplifiers that amplify different phase signals. However, amplifiers for amplifying, for example, millimeter wave signals may vary in phase according to an amplification factor due to parasitic capacitances. This may increase the phase error of an output signal from the phase shifter.
Thus, when the output signal of a phase shifter has a large phase error, it is difficult to implement a phased array system (beam forming or beam steering) used for millimeter wave communications or radar.
Incidentally, various phase shifters applied to phased array systems have been proposed in the past.
Patent Document 1: Japanese Laid-open Patent Publication No. H08(1996)-213878
Patent Document 2: Japanese Laid-open Patent Publication No. H08(1996)-213879
Patent Document 3: Japanese Laid-open Patent Publication No. 2001-244746
Patent Document 4: Japanese Examined Patent Application Publication No. S61(1986)-025255